Conventionally, a method of recording an image signal of an image-captured picture on a recording medium with it being made delayed using a memory having a large capacity has been proposed in Japanese patent application publication No. H09-83952. According to this method disclosed in the Japanese patent application publication No. H09-83952, it is possible to start recording from an image at a point of time retroacted by a set period of time from a point of time when a user instructs a start of image capture, thereby enabling a precious chance of image capture to be not missed.
Further, a method of recording a slow motion image by reducing a field frequency of an image signal using a memory has been proposed in Japanese Patent Application Publication No. 2005-295423. In other words, in this method disclosed in the Japanese Patent Application Publication No. 2005-295423, image signals are output at higher speed than that of a field frequency (50 or 60 fields/second) of a normal video signal and these image signals are successively stored in a memory in cyclical manner. These image signals thus stored in the memory are then read out thereof at the field frequency of the normal video signal and recorded on a recording medium. Hereinafter, such processing of obtaining any image-captured picture at a field or frame frequency higher than that of the normal video signal is referred to as “a high-speed image capture”.
Further, in conjunction with output of an image signal from an image-capturing device, a method of reducing a resolution of image-captured picture, namely, decreasing a number of pixels of the image-captured picture, which relates to the image signal output from the image-capturing device, thereby preventing data rate of the image signal from increasing has been proposed in Japanese Patent Application Publications Nos. S64-2480 and H01-105674. A method of preventing data rate from increasing by capturing a part of the image-captured picture has also been proposed in Japanese Patent Application Publication No. H10-51735.
However, when performing the high-speed image capture based on the method of the Japanese Patent Application Publication No. 2005-295423, a period of time for the high-speed image capture is limited in various ways, so that such a problem as to miss a precious chance of image capture can occur.
In other words, in this method, the image signal is stored in the memory at high speed and then, read out of the memory and recorded on the recording medium, so that a period of time that is available for capturing an image at one image capture chance can be limited by a capacitance of the memory. Accordingly, in a case where a desired scene is taken for a long period of time, it is after all difficult to perform the high-speed image capture on the whole scene. Further, in this method, it is impossible to perform image capture on a next scene after all the image signals stored in the memory would have been not read out thereof. Therefore, in a case where desired scenes are repeated at short intervals, taking a part of any repeated scenes may be missed.
As one method for solving such problem, a method of obtaining the image signal at high field or frame frequency and recording it on a mass recording medium directly is conceivable.
If, however, generating the image signal at high field or frame frequency, it is mostly difficult, in practical term, to generate the image signal indicating all the pixels from image-capturing device as a case where the image signal is generated at the field or frame frequency of the normal video signal. Accordingly, in this method, it is necessary, at a time of the high-speed image capture, to reduce a resolution of the image-captured picture on an image output from the image-capturing device as disclosed in the Japanese Patent Application Publications Nos. S64-2480 and H01-105674 or to decrease an angle of view in the image-captured picture as disclosed in the Japanese Patent Application Publication No. H10-51735. Thus, any image-captured picture having a desired resolution cannot be obtained, thereby causing deterioration in picture quality or causing an image-captured picture having a desired angle of view to be not obtained.